89 TPI car
The chug once again is hampering my fun factor. The problem is when the car gets warm/after a few heat soaks, it will stumble off launch eventually running correctly thru the rest of the gears. It is noticale at idle as the rpms will dips/bog/choke somewhat.

What I have done so far: rebuilt distributor, new TPS, new plugs, new fuel cap, new fuel tank vent, injectors ohm around upper 16 cold & upper 17 hot, replaced fuel pressure regulator w/ AFPR. Fuel pump (Edel 65gph) & filter are 1 year old, injectors are stock 305 injectors, no vac leaks whatsoever. The car has a difficult time starting initially, and after I'd turn the car off after a short run, the pump would continue to prime for 5 seconds or so. The FP with the stock FPR was about 20 KOEO. It didn't move much from there when the engine was on

Current Situation: after I put the AFPR on I did a long test at idle. I set FP at 43 psi w/ vac line detached. FP guage read 35 at idle and 40 when gassed. As I ran the car, then turned it off to soak, I noticed the FP would drop to 0 after 30 mins turned off. Each time I turned the car on, the FP would be less and less as the car got hotter. The last "run" had the car idling at 30psi and would not move when gassed.

My guess: is the fuel injectors which are stock. Could it be the fuel pump or filter? Why do I bleed so much pressure? I have the AFPR cranked all the way up.

I need a better set of eyes here. What am I missing in my logic?

 

Help please.....

 

I resolved a similar problem a few weeks ago. Didn't have any driveability problems, but water pump was failing and I replaced it. As I let the engine warm up with the new water pump, I saw my fuel presure was dropping the longer the car ran. I have the Holley AFPR, couln't get the pressure to rise for squat. Next day went out and monitered fuel pressure as the car warmed up in idle. I had excellent, adjustable pressure while cold, but again as the engine ran longer pressure dropped off. Replaced fuel pump (Racetronix), problem resolved. Do the fuel filter at the same time.

 

let it run until the pressure drops, then remove the return line and run it of into a gas can and restart. If the fuel pressure is still low and there is no return fuel then your pump is not delivering enough volume to maintain pressure. Check for internal tank leaks and replace pump anf filter if none are found.

 

Thanks guys,

Let me get another opinion on this; about a year ago I had that Edel 65 gph fuel pump put in. The guy dented my rocker panels and rendered my fuel tank vent/check valve useless. I tried to figure out why my tank wasn't venting for the longest time, eventually settling on a vented cap to band-aid the problem. I finally figured out the check valve was damaged and I replaced it and put the regular cap back on. So, rolling around with an inoperative vent for 9 months may have been the culprit in killing my new fuel pump? My problems began in the hottest month (July) last summer. That somewhat makes sense to me...can anyone validate my theory??

Thanks...
Eric

 

RVA? Reston?

Don't want to say change the fuel pump after only a year, it is a real PITA. However, the Holley AFPR's are known to drop pressure rapidly when off (is that what you have?), no real problem there. The in-tank fuel pumps are cooled by the fuel flowing through them. Loss of pressure as the pump runs longer is an indication the pump is going bad.

Hopefully someone else will chime in here.

 

Emission control laws require that fuel vapor be recirculated through the intake by way of the EVAP canister. You should not have or need a vented cap unless you've deleted the EVAP canister. Venting the fuel vapor through the gas cap affects your gas milage.

What you replaced wasn't the fuel tank pressure control valve.

1988 Corvette/Camaro; usage of an in-tank pressure control valve was terminated, which was part of the fuel tank sender assembly, and initiated usage of an underhood externally mounted tank pressure control valve.

EVAP canister is purged when:
Engine is warm.
After the engine has been running a specified time.
Above a specified road speed.
Above a specified throttle opening.

 

Well, whatever you call that cone-shaped vent thing, I replaced it as the old one was defective (after it got back from the pump install). That (along with the vented cap) cured my inflating gas tank problem. New vent-thing, regular cap, no problem there.

I guess that leads me back to trying to find out why this has happened. I would not doubt that this pump was somehow fouled up by the ineptness of the installer. I am not opposed to replacing it as I have replced everything except the injectors/filter/pump. I have avoided replacing the pump mostly due to it's age and degree of difficulty in doing the job myself.

Yes I do have a Holley AFPR on now. It helped a bit, until it started to get warm. More than likey I will replace the pump, but I was hoping for some kind of explination I could understand. Maybe it was just a bad pump.

Thanks for the guidance guys...
Eric

 

Yes it's possible for excessive tank pressure over time to cause fuel pump failure. I know that's not what you wanted to hear.
Heat shouldn't affect the pump as long as the tank is at least half-full, but will affect wire resistance which will require more current to drive the pump. I know wiring checks are a PITA and most leave it for last.
You suspect the pressure is bleeding off too fast, so start there before you do replace the pump.
Read this post:
https://www.thirdgen.org/forums/sear...earchid=416824
If you perform the pressure tests I posted (should be in any car manual with an intank pump) let's see the results.

 

your link is dead, but again thank you for a response

 

Try this one
https://www.thirdgen.org/forums/tech...very-lean.html

 

I did some initial "testing" before I really get into this and have a couple questions. I'm not hiding the fact that most everything I do, it is for the first time. (beginner auto hobbyist)

Step #3 ,mentions initial fuel pressure- with my NEW Holley AFPR turned all the way up, I can only muster 30 lbs. Then it took 13 minutes to reach 20 lbs. Does this change any of the parameters in this step?

Step #4, references the three items (fuel pump check valve, regulator diaph, leaky injectors)- I have a new FPR so I can rule that one out right? And where is the fuel pump check valve anyway?

Step #5, pinching fuel lines- my Chilton manual doesn't reference these, can you give me a hint as to which one is which or do I just need to pinch the one with the most resistance?

I will test more when i figure this stuff out. Beginning to think I have more than one issue here..

 

Measuring static output pressure and fuel delivery are the two standard diagnostic tests that can be used to determine a pump's ability to deliver fuel ,whether it's old, new, or remanufactured.

You suspect that there may be more than one issue, first test the pump's volumetric flow rate, if you've done it, what was the flow rate? Should be no less than 1/8gal (1pint) in 15seconds, or 1gal in 2 minutes.

It's not a good idea to rule anything out unless you've already tested it, or swapped for a known working unit.

Flow rate test procedure:
you could use a remote starter trigger switch, and one of those key shaped ALDL connector test jumpers.

A flexible hose long enough to reach outside of the engine bay and large enough to fit over the fuel supply line.

Line identification:The fuel supply line is connected to the end of the passenger side fuel rail and the fuel return line is connected to the fuel pressure regulator and runs along the top of the passenger side fuel rail.

1. Locate the ALDL diagnostic connector G-terminal (fuel pump test terminal with ignition key off.)
2. Connect one lead of the trigger to the G-terminal (insert one prong of the jumper key into the terminal and clamp the lead to it.)
3. Clamp the other lead of the trigger to a hot at all times 12v source (I use the postive lead on the back of the alternator.)
4. Use a suitable 2gal container, pinch the rubber section of the supply line to block the flow then disconnect it at the other end (engine side) and insert into the container using a long piece of flex hose.
5. Pull and hold the trigger for 2 minutes, then measure the volume in the container.

 

Again, your information is great, but I think you've taken me in another direction. I am still working on the first test set you gave me. I have enough "equipment" to do the first set of things but the second set is a bit over my head. Could we please back up and maybe steer your answers to my questions about the "Iroc Service Manual" items. I do not want to sound ungrateful, more like unqualified. Thank you for your patience.

 

The only qualification you need is patience, and the will to try and learn, that you've already demonstrated, and I'm willing if you have the time.
Can you identify the supply and return lines from what I provided? If so start at Step 5 and see how much change there is from the current initial 20psi. Note the time it takes from the time you clamp the line and the max pressure increase if, it increases at all.

The reason for the flow test is to isolate the tank and components, the fuel pump isn't the only thing that can fail in the tank.